This invention relates to knitting machines and particularly to circular knitting machines for the production of stockings, socks and like garments, possibly with the capability of creating patterns on the knitwear under electronic control. More particularly, the invention deals with a needle selector utilizing the piezoelectric effect for selectively actuating a multiplicity of needle jacks set on the surface of a knitting cylinder in such knitting machines
The piezoelectric needle selector is per se not new in the art and is disclosed in Japanese Laid-Open Utility Model Publication No. 63-167187. This known device includes an upstanding knitting cylinder rotatably mounted on the machine frame and carrying a multiplicity of needle jacks slidably received in as many guideways cut longitudinally in its surface. For selectively lifting the needle jacks on the revolving knitting cylinder, the prior art needle selector employs pairs of piezoelectric actuators or elements each in the shape of a thin strip of piezoelectric material supported in a cantilever fashion. Each pair of piezoelectric elements have pairs of plungers on their free ends for engaging one end of one of several needle select levers which are each medially supported for pivotal movement about a horizontal axis. Each needle select lever terminates at the other end in a finger of extremely hard alloy or ceramic material for acting on a butt of each selected needle jack on the knitting cylinder.
The knitting cylinder with the needle jacks thereon rotates at high speed in the operation of the knitting machine. Electric pulses are impressed to the piezoelectric elements as required by a desired knitting pattern to be created. Each pair of piezoelectric elements deflect by resonance vibration in response to signals of the required resonance frequencies supplied to their anode and cathode. Such resonance vibrations of the piezoelectric elements are imparted via the needle select levers to the needle jacks and hence to the knitting needles, causing the latter to travel up and down on the knitting cylinder. The desired pattern is thus formed on the fabric being knitted
The noted prior art device has proved to have certain shortcomings that must be overcome in order to establish true practical utility for the piezoelectric needle selector. First, being made of very thin plates, the piezoelectric elements have been susceptible to destruction due to the repeated application of stresses in use. They have also been unsatisfactory in the length of the stroke over which the needle jacks are moved between the working and retracted positions on the knitting cylinder, and in the force under which they are retained in either position Additionally, due to the lack of response and sufficiently high operating speed, the known needle selector has been prone to chattering, resulting in imperfections in the patterns created.